Reproduced signal processor and reproduced signal processing method

ABSTRACT

As shown in FIG.  1 , in the reproduced signal processing apparatus ( 100 ) of the present invention, the pattern predictor ( 103 ) predicts a predicted value which is a data sequence of a reproduced signal X and judges whether the predicted value matches a previously set specific pattern or not, and the adaptive equalizer ( 110 ) performs adaptive equalization on the reproduced signal X with timely updating the coefficients W of the digital filter according to the judgement result from the pattern predictor ( 103 ), and the selection circuit ( 104 ) outputs one of the output from the adaptive equalizer ( 110 ) and the predicted value as a waveform-equalized output Y on the basis of the judgement result.  
     The reproduced signal processing apparatus ( 100 ) so constructed can realize optimal waveform equalization for coping with the non-linear distortion included in the reproduced signal.

TECHNICAL FIELD

The present invention relates to a reproduced signal processingapparatus for equalizing a waveform of a reproduced signal which isreproduced from a recording medium and the reproduced signal processingmethod thereof.

BACKGROUND ART

A reproduction circuit for an optical disk, a magnetic disk and the likeis provided with an equalizer for performing waveform equalization of areproduced signal therein so as to eliminate a waveform distortion or anoise which is included in the reproduced signal, thereby compensatingintersymbol interference in the recording sequence. As the waveformequalization method, an adaptive equalization method in which thewaveform distortion is estimated from the reproduced signal to determinea characteristic for the equalizer is employed.

Here, with reference to FIG. 12, a reproduced signal for when arecording pit on an optical disk, a magnetic disk and the like is evenlyformed is compared with a reproduced signal for when a recording pit isuneven. FIG. 12 is a waveform diagram illustrating mark shapes and thereproduced signals for when the recording pit is evenly formed and forwhen the recording pit is uneven, respectively.

As shown in FIG. 12, when the recording pit is evenly formed, the markshape is completely rectangular. On the other hand, when the recordingpit is uneven, the mark shape has larger distortion on the both sides orat the center of the pit. When these signals are read by a pickup or thelike in the reproduction circuit, in a case where the recording pit isevenly formed, the level of the reproduced signal takes a constant valueat the center, and in a case where the recording pit is uneven, thelevel of the reproduced signal becomes distorted at the center, and thereproduced signal X becomes like a signal on which a frequency issuperimposed.

However, a prior art equalizer is constructed so as to perform onlylinear operations such as delaying the reproduced signals and performingmultiplication of coefficients and addition and is directed to eliminatelinear distortions of the reproduced signals. Therefore, when non-lineardistortion which is partly caused by production variances of a mediumsuch as an optical disk and a magnetic disk, or the like is included inthe reproduced signal (for example, refer to the reproduced signal forwhen the recording pit is uneven as shown in FIG. 12), the prior artequalizer cannot eliminate the distortion component. Then, thenon-linear distortion included in the reproduced signal substantiallyreduces the equalization ability of the equalizer, and thereforereduction in performance of the reproduction circuit such as degradationin bit error rate cannot be avoided.

As an apparatus for solving the problem of the prior art, a reproducedsignal processing apparatus for performing waveform equalizationprocessing taking into consideration an influence of the non-lineardistortion of the reproduced signal is disclosed in the Japanese PatentNo. 2768296.

Hereinafter, a prior art reproduced signal processing apparatus will bedescribed with using FIGS. 13, 14, and 15. FIG. 13 is a diagramillustrating a construction of the prior art reproduced signalprocessing apparatus, FIG. 14 is a diagram illustrating a detail of aconstruction of a digital filter in the prior art reproduced signalprocessing apparatus, and FIG. 15 is a diagram illustrating a detail ofa construction of a coefficient updater in the prior art reproducedsignal processing apparatus.

In FIG. 13, a prior art reproduced signal processing apparatus 400comprises a digital filter 401 and a coefficient updater 402. Then, thedigital filter 401 is a filter for receiving a reproduced signal Xobtained by digitizing a signal reproduced from an optical disk such asa CD and a DVD by a quantization section (not shown) in a reproductioncircuit, and here it is a FIR (Finite Impulse Response) filter of 5 tapsas shown in FIG. 14. Hereinafter, a detailed description will be givenwith using FIG. 14. The digital filter 401 comprises 5 D flip-flops 411a to 411 e connected to each other so as to constitute multiple stagesof delay elements each of which delays propagation of the reproducedsignal X, 5 multipliers 412 a to 412 e for multiplying the delayedsignals X₁ to X₅ outputted from the D flip-flops 411 a to 411 e bycoefficients W₁ to W₅, respectively, and an adder 413 for adding theoutputs from the respective multipliers 412. Therefore, the output X′ ofthe digital filter 401 is a value which is obtained by multiplying thedelayed signals X₁ to X₅ obtained by delaying the reproduced signal X bythe coefficients W₁ to W₅, respectively, and adding all themultiplication resultants in the adder 413.

Then, the coefficient updater 402 adaptively updates the coefficients W₁to W₅ for determining an equalization characteristic for the digitalfilter 401 according to the output of the digital filter 401, and herethe coefficient updater 402 comprises a correlation unit 421, anintegrator 422, a subtracter 423, a reference amplitude generationcircuit 424, a ternary discrimination circuit 425, an error signalselection circuit 426, and a switch 427, as shown in FIG. 15. Then, theternary discrimination circuit 425 makes a discrimination as to thedigital filter output X′ which is output from the digital filter 401 toassign one of three values (for example, −1, 0, +1) to the output X′according to a predetermined threshold value, the reference amplitudegeneration circuit 424 converts the three values (for example, −1, 0,+1) output from the ternary discrimination circuit 425 into amplitudevalues corresponding to the output levels of the digital filter 401,respectively, the subtracter 423 calculates an equalization error εwhich is a difference between an output of the reference amplitudegeneration circuit 424 and the digital filter output X′, the correlationunit 421 takes a correlation between a delayed signal X_(n) which isinput from the digital filter 401 and an equalization error ε_(n) fromthe subtracter 423, the integrator 422 supplies a value obtained bytime-integrating each of the correlations taken by the correlation unit421 as an updated coefficient W_(n), to the digital filter 401, theerror signal selection circuit 426 generates a selection signal forselecting whether or not the equalization error ε calculated by thesubtracter 423 is to be input to the correlation unit 421, on the basisof the time-series information of output from the ternary discriminationcircuit 425, and the switch 427 switches between on and off, accordingto the selection signal from the error signal selection circuit 426.

In such a prior art reproduced signal processing apparatus 400, thecoefficient updater 402 previously sets distinctive patterns which seemto have non-linear distortions from among the outputs of the ternarydiscrimination circuit 425 in the error signal selection circuit 426,and the error signal selection circuit 426 judges whether or not thepreviously set distinctive patterns match the outputs from the ternarydiscrimination circuit 425. When there is no matching, the error signalselection circuit 426 turns on the switch 427 to update the coefficientsW₁ to W₅. When there is a matching, the error signal selection circuit426 turns off the switch 427 so as not to update the coefficients W₁ toW₅. Thereby, an influence which the non-linear distortion of thereproduced signal X exerts on the update of the coefficients W₁ to W₅can be controlled.

However, a failure in the waveform equalization is not caused only bythe above-described adaptive control of the coefficient update in thecoefficient updater 402, and there are some cases where the digitalfilter output X′ subjected to waveform equalization by the digitalfilter 401 (hereinafter, also referred to as “waveform-equalized outputX′”) itself is a cause of the failure in waveform equalization.

Hereinafter, a specific description will be given with using FIG. 16.FIG. 16 is a diagram illustrating a reproduced signal X inclusive ofnon-linear distortion and a waveform-equalized output Y obtained byadaptively equalizing the reproduced signal X.

As described with reference to FIG. 12, a reproduced signal having largenon-linear distortion may be a signal on which a signal in a certainfrequency band which is not included in normal waveform of thereproduced signal is superimposed. In a case where the superimposedfrequency band is far from the frequency band of the reproduced signal,the digital filter 401 can easily eliminate the superimposed signal. Onthe other hand, in a case where the superimposed frequency band is closeto the frequency band of the reproduced signal, it cannot be determinedwhether the large distortion of the waveform of the reproduced signal isa waveform distortion due to non-linear distortion or normal waveform ofthe reproduced signal, and therefore it becomes very difficult tocorrect the non-linear distortion of the waveform.

For example, A, B, and D portions among A to D portions which are largedistortions of the waveform of the reproduced signal X as shown in FIG.16 are non-linear distortions which are caused by superimposing a normalwaveform on a signal of the same frequency band as that of the normalwaveform, and C portion is a normal waveform of the reproduced signal.When the prior art apparatus 400 subjects such a waveform to waveformequalization, in a case where the reproduced signal X has a distortioncomponent of the same frequency band as that of the normal waveformportion, even when the coefficients W₁ to W₅ are not updated for thedistortion portion, the distortion component of the reproduced signalitself is similarly amplified, thereby resulting in failure in thewaveform equalization (refer to the A, B, and D portions in FIG. 16).Then, when the constraints for coding is satisfied, even a post-stagedecoder such as a Viterbi decoder not shown cannot correct the error andthen the reproduced signal may be decoded as it is, and therefore thefailure in the waveform equalization is a cause of the degradation inthe decoding performance of the reproduction circuit.

Accordingly, even if the coefficients W₁ to W₅ are not updated for theportions which seem to be non-linear distortions of the waveform of thereproduced signal X as in the prior art reproduced signal processingapparatus 400, there are some cases where influence of non-lineardistortion on the waveform-equalized output X′ cannot be controlled. Asa result, in the prior art reproduced signal processing apparatus 400,the digital filter 401 cannot have a waveform equalizationcharacteristic which sufficiently copes with the non-linear distortionand there is a problem that the reproduced signal including non-lineardistortion cannot be optimally waveform-equalized.

The present invention is made in view of the above-described problemsand its object is to provide a reproduced signal processing apparatuswhich copes with a non-linear distortion included in a reproduced signaland can realize optimal waveform equalization.

DISCLOSURE OF THE INVENTION

In order to solve the above-described problems, a reproduced signalprocessing apparatus according to the present invention is a reproducedsignal processing apparatus for equalizing a waveform of a reproducedsignal which is reproduced from a recording medium which comprises: adigital filter for equalizing the reproduced signal; a coefficientupdater for adaptively updating coefficients for determining anequalization characteristic of the digital filter; a pattern predictorfor predicting a data sequence of the reproduced signal and outputting apredicted value of the reproduced signal, and judging whether or not thedata sequence of the reproduced signal is a previously set specificpattern, thereby to output the judgement result; and a selection circuitfor selecting one of the output of the digital filter and the predictedvalue of the reproduced signal as a waveform-equalized output, andoutputting the selected one.

Therefore, the reproduced signal is adaptively equalized, and thereafterone of the adaptively equalized output and the data sequence predictedfrom the reproduced signal is selected and outputted as awaveform-equalized output, thereby realizing optimal waveformequalization for coping with non-linear distortion included in thereproduced signal.

Further, in the reproduced signal processing apparatus according to thepresent invention, the selection circuit selects the output of thedigital filter when the judgement result indicates that the datasequence of the reproduced signal is the specific pattern, and selectsthe predicted value when the judgement result indicates that the datasequence of the reproduced signal is not the specific pattern.

Therefore, the influence which the non-linear distortion included in thereproduced signal exerts on the waveform-equalized output can beoptimally controlled.

Further, in the reproduced signal processing apparatus according to thepresent invention, the coefficient updater updates the coefficients ofthe digital filter when the judgement result indicates that the datasequence of the reproduced signal is the specific pattern, and does notupdate the coefficients of the digital filter when the judgement resultindicates that the data sequence of the reproduced signal is not thespecific pattern.

Therefore, the influence which the non-linear distortion included in thereproduced signal exerts on the update of the coefficients of thedigital filter can be controlled.

Further, in the reproduced signal processing apparatus according to thepresent invention, the coefficient updater adaptively updates thecoefficients of the digital filter using the predicted value.

Therefore, the influence which the non-linear distortion included in thereproduced signal exerts on the update of the coefficients of thedigital filter can be optimally controlled.

Further, in the reproduced signal processing apparatus according to thepresent invention, the digital filter equalizes the reproduced signalinto multiple values and outputs the equalized signal, and the specificpatterns which are previously set in the pattern predictor are portionsin which the data sequence of the reproduced signal changes from aminimum value up to a maximum value and in which it changes from themaximum value up to the minimum value.

Therefore, even when the non-linear distortion of the same frequencyband as that of the normal waveform of the reproduced signal isincluded, the influence which the non-linear distortion exerts on thewaveform-equalized output can be controlled, thereby performing waveformequalization optimally.

Further, in the reproduced signal processing apparatus according to thepresent invention, the digital filter equalizes the reproduced signalinto multiple values and outputs the equalized signal, and the specificpattern which is previously set in the pattern predictor is a portion inwhich the data sequence of the reproduced signal is other than theminimum value and the maximum value.

Therefore, even when the non-linear distortion of the same frequencyband as that of the normal waveform of the reproduced signal isincluded, the influence which the non-linear distortion exerts on thewaveform-equalized output can be controlled, thereby performing waveformequalization optimally.

Further, in the reproduced signal processing apparatus according to thepresent invention, the pattern predictor predicts the data sequence ofthe reproduced signal using partial response equalization, and judgeswhether the predicted data sequence of the reproduced signal matches thespecific pattern or not.

Therefore, even when the non-linear distortion of the same frequencyband as that of the normal waveform of the reproduced signal isincluded, the influence which the non-linear distortion exerts on thewaveform-equalized output can be controlled, thereby performing waveformequalization optimally.

Further, a reproduced signal processing apparatus according to thepresent invention is a reproduced signal processing apparatus forequalizing a waveform of a reproduced signal which is reproduced from arecording medium, which comprises: a pattern predictor for judgingwhether or not the data sequence of the reproduced signal is apreviously set specific pattern, thereby to output the judgement result;a prediction filter for partially performing filtering on the reproducedsignal on the basis of the judgement result; and an adaptive equalizerfor adaptively equalizing the output of the prediction filter.

Therefore, the reproduced signal is partially subjected to filtering andis then adaptively equalized, thereby realizing optimal waveformequalization for coping with the non-linear distortion included in thereproduced signal.

Further in the reproduced signal processing apparatus according to thepresent invention, the pattern predictor makes judgement as to the datasequence of the reproduced signal and predicts the data sequence of thereproduced signal to output the predicted value of the reproducedsignal; the prediction filter outputs the reproduced signal when thejudgement result indicates that the data sequence of the reproducedsignal is the specific pattern; and outputs the predicted value of thereproduced signal when the judgement result indicates that the datasequence of the reproduced signal is not the specific pattern.

Therefore, even when the non-linear distortion of the same frequencyband as that of the normal waveform of the reproduced signal isincluded, the influence which the non-linear distortion exerts on thewaveform-equalized output can be controlled, thereby performing waveformequalization optimally.

Further, in the reproduced signal processing apparatus according to thepresent invention, the filtering processing performed by the predictionfilter is to eliminate a specific frequency band from the waveform ofthe reproduced signal only when the judgement result indicates that thedata sequence of the reproduced signal is not the specific pattern.

Therefore, the influence of the filtering does not occur except in theportions of the specific patterns of the data sequence of the reproducedsignal, thereby supplying a signal having little non-linear distortionto the adaptive equalizer in the post stage.

Further, in the reproduced signal processing apparatus according to thepresent invention, the specific patterns which are previously set in thepattern predictor are portions in which the predicted data sequence ofthe reproduced signal changes from a minimum value up to a maximum valueand in which it changes from the maximum value up to the minimum value.

Therefore, even when the non-linear distortion of the same frequencyband as that of the normal waveform of the reproduced signal isincluded, the influence which the non-linear distortion exerts on thewaveform-equalized output can be controlled, thereby performing waveformequalization optimally.

Further, in the reproduced signal processing apparatus according to thepresent invention, the specific pattern which is previously set in thepattern predictor is a portion in which the predicted data sequence ofthe reproduced signal is other than the minimum value and the maximumvalue.

Therefore, even when the non-linear distortion of the same frequencyband as that of the normal waveform of the reproduced signal isincluded, the influence which the non-linear distortion exerts on thewaveform-equalized output can be controlled, thereby performing waveformequalization optimally.

Further, a reproduced signal processing method according to the presentinvention is a reproduced signal processing method for equalizing awaveform of a reproduced signal which is reproduced from a recordingmedium, which comprises: an adaptive equalization step of adaptivelyequalizing the reproduced signal with updating coefficients fordetermining an equalization characteristic of the waveform, thereby tooutput the equalized signal; a prediction step of predicting the datasequence of the reproduced signal and outputting the predicted value ofthe reproduced signal; a judgement step of judging whether or not thedata sequence of the reproduced signal is a previously set specificpattern, thereby to output the judgement result; and a selection step ofselecting one of the output of the equalization step and the output ofthe prediction step as a waveform-equalized output, and outputting theselected one.

Therefore, one of the reproduced signal which was adaptively equalizedand the predicted value which is predicted from the reproduced signal isselected and outputted as a waveform-equalized output, thereby realizingoptimal waveform equalization for coping with non-linear distortionincluded in the reproduced signal.

Further, a reproduced signal processing method according to the presentinvention is a reproduced signal processing method for equalizing awaveform of a reproduced signal which is reproduced from a recordingmedium, which comprises: a judgement step of judging whether or not thedata sequence of the reproduced signal is a previously set specificpattern, thereby to output the judgement result; a filtering step ofpartially performing filtering on the reproduced signal on the basis ofthe judgement result; and an adaptive equalization step of adaptivelyequalizing the output of the filtering step.

Therefore, the reproduced signal is subjected to filtering, andthereafter the output which was subjected to filtering can be adaptivelyequalized, thereby realizing optimal waveform equalization for copingwith non-linear distortion included in the reproduced signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a construction of a reproduced signalprocessing apparatus according to a first embodiment of the presentinvention.

FIG. 2 is a diagram illustrating a detail of a construction of acoefficient updater in the reproduced signal processing apparatusaccording to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a detail of a construction of a patternpredictor in the reproduced signal processing apparatus according to thefirst embodiment of the present invention.

FIG. 4 is a waveform diagram illustrating an operation of the patternpredictor in the reproduced signal processing apparatus according to thefirst embodiment of the present invention.

FIG. 5 is a waveform diagram showing reproduced signals and predictedvalues thereof in a case where a reproduced signal to be input to thereproduced signal processing apparatus is normal (Xa) and in a casewhere a reproduced signal to be input to the reproduced signalprocessing apparatus has a large non-linear distortion (Xb),respectively, according to the first embodiment of the presentinvention.

FIG. 6 is a diagram for explaining an operation of the coefficientupdater in the reproduced signal processing apparatus according to thefirst embodiment of the present invention.

FIG. 7 is a diagram for explaining an operation of a selection circuitin the reproduced signal processing apparatus according to the firstembodiment of the present invention.

FIG. 8 is a waveform diagram showing a reproduced signal which is inputto the reproduced signal processing apparatus, predicted values of thereproduced signal, and a waveform-equalized output obtained byequalizing the reproduced signal, according to the first embodiment ofthe present invention.

FIG. 9 is a diagram illustrating a construction of a reproduced signalprocessing apparatus according to a second embodiment of the presentinvention.

FIG. 10 is a waveform diagram illustrating an operation of a predictionfilter in the reproduced signal processing apparatus according to thesecond embodiment of the present invention.

FIG. 11 is a waveform diagram illustrating an operation of a predictionfilter of a modification of the reproduced signal processing apparatusaccording to the second embodiment of the present invention.

FIG. 12 is a diagram illustrating mark shapes and the reproduced signalsfor when a recording pit to be recorded on a recording medium is evenand for when a recording pit is uneven, respectively.

FIG. 13 is a diagram illustrating a construction of a prior artreproduced signal processing apparatus.

FIG. 14 is a diagram illustrating a detail of a construction of adigital filter in the prior art reproduced signal processing apparatus.

FIG. 15 is a diagram illustrating a detail of a construction of acoefficient updater in the prior art reproduced signal processingapparatus.

FIG. 16 is a waveform diagram illustrating a reproduced signal which isinput to the prior art reproduced signal processing apparatus andwaveform-equalized output obtained by equalizing the reproduced signal.

BEST MODE TO EXECUTE THE INVENTION Embodiment 1

Hereinafter, a reproduced signal processing apparatus according to afirst embodiment will be described with reference to FIGS. 1 to 8 and14.

In the first embodiment, in a case where a reproduced signal includingnon-linear distortion is adaptively equalized, the influence of thenon-linear distortion is considered not only for the update ofcoefficients W₁ to W₅ for determining an equalization characteristic ofa digital filter, but also for adaptively-equalized waveform-equalizedoutput which is outputted from the digital filter.

Initially, a construction of the reproduced signal processing apparatusaccording to the first embodiment will be described with reference toFIGS. 1 to 3 and 14. FIG. 1 is a diagram illustrating a construction ofthe reproduced signal processing apparatus according to the firstembodiment, FIG. 2 is a diagram illustrating a detail of a constructionof a coefficient updater of the reproduced signal processing apparatusaccording to the first embodiment, and FIG. 3 is a diagram illustratinga detail of a construction of a pattern predictor of the reproducedsignal processing apparatus according to the first embodiment.

In FIG. 1, the reproduced signal processing apparatus 100 according tothe first embodiment comprises an adaptive equalizer 110 including adigital filter 101 and a coefficient updater 102, a pattern predictor103, and a selection circuit 104.

Then, the digital filter 101 of the adaptive equalizer 110 receives areproduced signal X obtained by digitizing a signal reproduced from anoptical disk such as a CD and a DVD in a quantization circuit (notshown) which is in a previous stage of the adaptive equalizer 110. Thecoefficient updater 102 adaptively updates the coefficients W₁ to W₅ fordetermining an equalization characteristic of the digital filter 101according to the reproduced signal X, a predicted value P and ajudgement result of the pattern predictor 103, which will be describedlater, and an output X′ of the digital filter 101. The adaptiveequalizer 110 adaptively equalizes the reproduced signal X in thedigital filter 101 with using the coefficient W which has been timelyupdated by the coefficient updater 102. Then, in the first embodiment,the digital filter 101 is constructed as a FIR (Finite Impulse Response)filter of 5 taps shown in FIG. 14 like the prior art digital filter 401described above, and the number of coefficients W which are timelyupdated by the coefficient updater 102 is 5 (W₁ to W₅).

Then, the pattern predictor 103 predicts a binary data sequence (apredicted value P) obtained from the reproduced signal X, and judgeswhether or not the predicted value P which is the predicted datasequence matches a previously set specific pattern, thereby outputtingthe judgement result. Further, the selection circuit 104 receives adigital filter output X′ from the digital filter 101, and the predictedvalue P and the judgement result from the pattern predictor 103, andoutputs one of the digital filter output X′ and the predicted value P asa waveform-equalized output Y on the basis of the judgement result.

Hereinafter, the details of the constructions of the coefficient updater102 and the pattern predictor 103 will be described with using FIGS. 2and 3, respectively.

Initially, as shown in FIG. 2, the coefficient updater 102 comprises asubtracter 221 for calculating an equalization error ε_(n) which is adifference between a digital filter output X′_(n) which is output fromthe digital filter 101 and a predicted value P_(n), a multiplier 222 fortaking a correlation between each delayed signal X_(n) obtained bydelaying the reproduced signal X by the D flip-flop in the digitalfilter 101 for taking a clock delay into consideration and anequalization error ε_(n) from the subtracter 221, an amplifier 223 foramplifying the output from the multiplier 222 at an amplification factorμ, an adder 224 for adding the output from the amplifier 223 and the(n−1)th coefficient W_(n-1) and outputting the updated coefficientW_(n), and a control circuit 225 for controlling whether or not theupdated coefficient W_(n) is to be output from the adder 224 on thebasis of the judgement result from the prediction pattern determinationunit 103. Under the control of the control circuit 225, the coefficientW_(n) is updated so that the second power of the equalization errorε_(n) is minimized, thereby adaptively controlling the equalizationcharacteristic of the digital filter 101 according to the waveformcharacteristic of the reproduced signal X. Then, while the coefficientupdater 102 shown in FIG. 2 is constructed so as to update only onecoefficient W in one update, all the coefficients W_(n-4), W_(n-3),W_(n-2), W_(n-1), W_(n) (here, coefficients W₁ to W₅) can be updated inone update when the similar circuits are provided by the number ofcoefficients W_(n) (here 5 pieces).

As shown in FIG. 3, the pattern predictor 103 comprises D flip-flops 231a to 231 d each of which delays the reproduced signal X by one clock, anadder 232 for adding the reproduced signal X and the signal which isobtained by delaying the reproduced signal X by one clock in the Dflip-flop 231 a, a sign unit 233 for calculating a sign of the outputfrom the adder 232, an adder 234 for adding the output from the signunit 233, and the outputs each of which is obtained by delaying theoutput from the sign unit 233 by one clock in each of the three Dflip-flops 231 b to 231 d, thereby executing PR (1,1,1,1), a predictedvalue memory 235 for outputting a predicted value P on the basis of theresult of the PR (1,1,1,1), and a judgement unit 236 for judging whetherthe predicted value P is a previously set specific pattern or not. Usingthe partial response PR (1,1,1,1), the pattern predictor 103 predicts adata sequence of the reproduced signal X to output a predicted value P,and judges whether the predicted value P is the previously set specificpattern or not, thereby outputting the judgement result. Then, the PR(1,1,1,1) is a signal obtained from 1+D₁+D₂+D₃, and D_(m(m=1 to 3)) is asignal which is obtained by delaying the reproduced signal X by mclocks. Then, the binary data sequence of the reproduced signal X whichwas equalized into multiple values (predicted value P) can be obtainedby using the PR (1,1,1,1) because signals of DVD are coded in themodulation/demodulation scheme of EFM+, and the signals of DVD arerecorded in the modulation scheme called NRZI (Non Return to ZeroInverted) at the recording.

Next, a series of operations of the reproduced signal processingapparatus of the above-described construction according to the firstembodiment will be described with reference to FIGS. 4 to 8. FIG. 4 is adiagram illustrating values obtained by the respective sections of thepattern predictor according to the first embodiment.

Initially, a reproduced signal X which is digitized by the quantizationmeans not shown is input to the adaptive equalizer 110 and the patternpredictor 103.

In the adaptive equalizer 110, the digital filter 101 performs adaptiveequalization according to the coefficients W₁ to W₅ which are suppliedfrom the coefficient updater 102 on the input reproduced signal X as inthe prior art apparatus 400 which has been previously described, andoutputs the equalized digital filter output X′ to the selection circuit104.

At the same time, the pattern predictor 103 predicts a data sequence ofthe input reproduced signal X to output the predicted data sequence as apredicted value P of the reproduced signal X to the selection circuit104, and simultaneously judges whether or not the predicted value Pmatches the previously set specific pattern and outputs the judgementresult to the coefficient updater 102 and the selection circuit 104.

Hereinafter, the operation of the pattern predictor 103 will bedescribed in detail with using FIG. 4. Initially, when a reproducedsignal X having a value as shown in FIG. 4 is input to the patternpredictor 103, the reproduced signal X is delayed by one clock by the Dflip-flop 231 a and thereafter the delayed reproduced signal X is addedto the reproduced signal X to obtain a value (1+D) X by the adder 232.Here, (1+D) is calculated initially so as to easily realize a functionsimilar to that of an interpolation filter implemented by a Nyquistfilter. Here, by performing operation (1+D), a level equivalent to thatof the intermediate point of 2 adjacent sampling points is obtained.Then, the Nyquist filter may be constructed by a FIR filter of pluraltaps.

Subsequently, the value (1+D)X output from the adder 232 is input to thesign unit 233, and the sign unit 233 obtains a value of sign (1+D)X.Here, when the value of output (1+D)X of the adder 232 is negative, thevalue of sign (1+D)X is set to “0”, and when the value is not negative,the value of sign (1+D)X is set to “1”.

Then, the value of sign (1+D)X output from the sign unit 233 is delayedby one clock in the D flip-flops 231 b to 231 d, respectively, and theadder 234 adds the output of the sign unit 233 and the respectiveoutputs from the D flip-flops 231 b to 231 d to obtain a value of PR(1,1,1,1). Here, since the value of PR (1,1,1,1) is obtained by delayingthe reproduced signal X by one clock in the D flip-flops 231 a to 231 d,respectively, and adding all the delayed values by the adder 234, thevalue of PR (1,1,1,1) output from the adder 234 takes values of “0” to“4” as shown in FIG. 4.

The value of PR (1,1,1,1) always changes from the previous value only by+1, −1 or 0 because of a characteristic of DVD reproduced signal.Accordingly, when the reproduced signal X to be input to the reproducedsignal processing apparatus 100 is a DVD reproduced signal, a value PR(1,1,1,1) of the signal, which is predicted from the reproduced signalX, changes to such as 0→0→1→2→3→4→4→4→3→2→1→2→3→4, and the value PRnever changes to such as 0→4→2→4→1→3.

Then, the predicted value memory 235 outputs a predicted value P whichis a predicted data sequence of the reproduced signal X on the basis ofthe output from the adder 234. Here, the values corresponding to outputvalues, 0, 1, 2, 3, and 4, of the adder 234 are −44, −25, 0, 25, and 44,respectively, and in the predicted value memory 235, the five values areapplied correspondingly to the inputted output value PR (1,1,1,1) of theadder 234, and the value is output as predicted value P of thereproduced signal X. 5 values corresponding to the output values of theadder 234 are thus provided as the predicted value P so that thepredicted value P falls within a range of the values which thereproduced signal X can take. Thereby, the waveform-equalized output Ywhich is outputted from the reproduced signal processing apparatus 100of the first embodiment is equalized into these 5 values. Then, fivevalues (−44, −25, 0, 25, 44) are described here as an example, and anyvalue which the reproduced signal X can take may be used. Further, whilein the first embodiment what outputs the predicted value P is referredto as a predicted value memory 235, it is not restricted to a memory,and whatever has the same function as that of the predicted value memory235, for example, a combination of a register and a multiplexer, can beused.

Here, comparing the predicted value P of the reproduced signal Xobtained as above-described for when the reproduced signal X is normal(waveform Xa) and that for when the reproduced signal X has largenon-linear distortion (waveform Xb), as shown in FIG. 5, when a signalas a reference, for example, 0 (zero) level, is being maintainedconstant by an offset canceller not shown regardless of whether thenon-linear distortion is present or not, the predicted value P of thereproduced signal is the same regardless of whether the waveformdistortion of the reproduced signal is large or small. It is apparentalso from the contents of the operation of the pattern predictor 103,that is, the contents that the PR (1,1,1,1) is executed with using signof the intermediate point of 2 adjacent sampling points.

Then, the predicted value P of the reproduced signal X which is outputfrom the predicted value memory 235 is output to the judgement unit 236,and the judgement unit 236 judges whether the predicted value P matchesthe previously set specific pattern or not.

For example, a portion in which the predicted value P changes up to amaximum value, or up to a minimum value, that is, a portion in which thepredicted value P changes to “−25”, “0”, “25” is previously set as thespecific pattern in the judgement unit 236, and in a case where ajudgement result that an edge is to be raised is output when the changeof the predicted value P matches the specific pattern, the judgementunit 236 outputs the judgement result that a portion in which thepredicted value P changes to “−25”, “0”, “25” should be an edge portion,as a judgement result, as shown in FIG. 4. Then, while in the firstembodiment, the predicted value P which is an output from the predictedvalue memory 235 is input to the judgement unit 236, the output of theadder 234 may be input to the judgement unit 236 since the output values(0 to 4) of the adder 234 correspond to and are equivalent to thepredicted values P (−44, −25, 0, 25, 44) as described above. In thiscase, a portion in which the output value of the adder 234 changes to“1”, “2”, “3” is previously set as a specific pattern in the judgementunit 236, thereby obtaining the same result as that for the case wherethe portion in which the predicted value changes to “−25”, “0”, “25” isset as the specific pattern as described above.

Then, the judgement result so obtained is output to the control circuit225 in the coefficient updater 102 and the selection circuit 104, andthe control circuit 225 in the coefficient updater 102 controls whetheror not the coefficients W₁ to W₅ should be updated according to thejudgement result, and the selection circuit 104 selects which of thedigital filter output X′ and the predicted value P of the reproducedsignal X is to be output as a waveform-equalized output Y according tothe judgement result.

Initially, a case where the judgement result is used to update thecoefficients W₁ to W₅ will be described with reference to FIG. 6. FIG. 6is a diagram for explaining a judgement method executed by the judgementunit at the updating of the coefficient according to the firstembodiment. Then, “learning” shown in FIG. 6 is to adaptively change theequalization characteristic, that is, to execute the update of thecoefficient, while “non-learning” is to unchange the equalizationcharacteristic, that is, to execute no update of the coefficient.

For example, in a case where a portion in which the predicted value Pchanges from a maximum value up to a minimum value, and a portion inwhich the predicted value P changes from a minimum value up to a maximumvalue, are set as the specific patterns, a signal A shown in FIG. 6 isoutput as the judgement result from the judgement unit 236 in thepattern predictor 103. Then, in a case where a portion in which thepredicted value P is other than the maximum value and the minimum value,is set as the specific pattern, a signal B shown in FIG. 6 is output asthe judgement result from the judgement unit 236 in the patternpredictor 103.

Then, when the control circuit 225 in the coefficient updater 102receives the judgement result obtained as described above, the controlcircuit 225 in the coefficient updater 102 performs control so that theupdate of the coefficients W₁ to W₅ is not adaptively executed accordingto the reproduced signal X in the “non-learning” period (a non-edgeportion), while the control circuit 225 performs control so that theupdate of the coefficients W₁ to W₅ is executed in the “learning” period(an edge portion). Therefore, even when a reproduced signal of largenon-linear distortion is input, the inappropriate coefficient update dueto the non-linear distortion can be avoided, thereby improving theconvergence of the coefficient update.

Next, a case where the judgement result is used for the waveformequalization will be described with reference to FIG. 7. FIG. 7 is adiagram for explaining the judgement method executed by the judgementunit at the waveform equalization according to the first embodiment.Here, the judgement result signal B shown in FIG. 6 is taken as anexample.

As described above, the judgement result obtained by the judgement unit236 in the pattern predictor 103 is output to the selection circuit 104.Then, the selection circuit 104 outputs digital filter output X′ as awaveform-equalized output Y in a portion in which the predicted value Pof the reproduced signal changes to “−25”, “0”, “25”, and outputs thecorresponding predicted value P, instead of the digital filter outputX′, as a waveform-equalized output Y except in a portion where thepredicted value P of the reproduced signal changes to “−25”, “0”, “25”,on the basis of the judgement result from the pattern predictor 103.

This is done by utilizing the fact that whether the waveform of thereproduced signal is normal (waveform Xa) or the waveform includesnon-linear distortion (waveform Xb), the predicted value P is the same,as previously described with reference to FIG. 5. Thus, when thepredicted value P generated from the reproduced signal X is output as awaveform-equalized output Y instead of the digital filter output X′ in aportion in which the waveform of the reproduced signal X may includenon-linear distortion, waveform equalization can be performed withoutfailure in waveform equalization even in a portion in which the priorart apparatus 400 might have failed to perform waveform equalization asin an area circled by dotted lines shown in FIG. 8.

As described above, according to the first embodiment, the patternpredictor 103 creates a predicted value P of a reproduced signal X aswell as judges whether the predicted value P is a previously setspecific pattern or not. The reproduced signal X is subjected toadaptive equalization in the adaptive equalizer 110, and thereafter theselection circuit 104 selects one of the output from the adaptiveequalizer 110 and the predicted value P of the reproduced signal fromthe pattern predictor 103 according to the judgement result, thereby tooutput the selected one as a waveform-equalized output Y. Therefore,even when the reproduced signal X which is input to the reproducedsignal processing apparatus of the first embodiment has a waveformhaving non-linear distortion, on which a frequency component of the sameband as that of the normal waveform is superimposed as described withreference to FIG. 16, the failure in waveform equalization caused by thenon-linear distortion is eliminated, thereby suppressing the influenceof the waveform distortion on the waveform-equalized output Y. As aresult, in the reproduced signal processing apparatus 100 of the firstembodiment, the preferable equalization characteristic can be obtainedand the reproduced signal X can be always subjected to optimal adaptiveequalization.

Then, while in the first embodiment a case where the number ofcoefficients W_(n) for determining an equalization characteristic of thedigital filter 101 is five is taken as an example, the number ofcoefficients W is not restricted thereto.

Embodiment 2

Hereinafter, a reproduced signal processing apparatus according to asecond embodiment will be described with reference to FIGS. 9 and 10.

While in the above-described first embodiment a reproduced signal X isadaptively equalized by an adaptive equalizer initially, and thereaftera selection circuit in the post stage selects one of an output of theadaptive equalizer (digital filter output X′) and a predicted value P ofthe reproduced signal X which is predicted by a pattern predictor,thereby outputting a waveform-equalized output Y in which a non-lineardistortion has been eliminated, a non-linear distortion of thereproduced signal X is eliminated through a filter, and thereafter anadaptive equalizer in the post stage adaptively equalizes the signal inwhich the non-linear distortion has been eliminated, in this secondembodiment.

Initially, a construction of the reproduced signal processing apparatusaccording to the second embodiment will be described using FIG. 9.

In FIG. 9, a reproduced signal processing apparatus 300 according to thesecond embodiment comprises an adaptive equalizer 301, a predictionfilter 302, and a pattern predictor 303. The adaptive equalizer 301adaptively changes the equalization characteristic thereof according tothe output from the prediction filter 302 described later, and performswaveform equalization on the output from the prediction filter 302, andthe adaptive equalizer 301 mainly comprises a digital filter and acoefficient updater which updates coefficients W_(n) (n is an integer)for determining an equalization characteristic of the digital filter. Asan example of a specific construction of the adaptive equalizer, anadaptive equalizer comprising a conventional digital filter 401 andcoefficient updater 402 or an adaptive equalizer comprising a digitalfilter 101 and coefficient updater 102 which are described in the firstembodiment may be taken.

Then, the pattern predictor 303 predicts a binary data sequence (apredicted value P) obtained from the reproduced signal X, and judgeswhether or not the predicted value P matches a previously set specificpattern to output the judgement result. The construction and operationof the pattern predictor 303 are the same as those of the patternpredictor 103 of the first embodiment.

Then, the prediction filter 302 subjects the reproduced signal X tofiltering and the contents of the filtering to be executed is determinedby the pattern predictor 303, and here one of the reproduced signal Xand the predicted value P of the reproduced signal X which is predictedby the pattern predictor 303 is output according to the judgement resultoutputted from the pattern predictor 303. As a construction of theprediction filter 302, for example, a selection circuit for selectingthe output value according to the judgement result is assumed.

Next, a series of operations of the reproduced signal processingapparatus 300 of the above-described construction according to thesecond embodiment will be described using FIG. 10. FIG. 10 is a waveformdiagram for explaining the filtering performed by the prediction filterin the reproduced signal processing apparatus according to the secondembodiment.

Initially, a reproduced signal X which is digitized by the quantizationmeans not shown is input to the prediction filter 302 and the patternpredictor 303.

The predicted value P and the judgement result are created from thereproduced signal X which is input to the pattern predictor 303 asdescribed in the first embodiment, and outputted to the predictionfilter 302. Here, a portion in which the predicted value P is other thana maximum value and a minimum value is set as a previously set specificpattern, and a signal B shown in FIG. 6 is output as the judgementresult from the judgement unit 236 in the pattern predictor 303.

Then, the prediction filter 302 outputs one of the reproduced signal Xand the predicted value P as a prediction filter output on the basis ofthe judgement result.

Hereinafter, a specific description will be given using FIG. 10.Initially, when the reproduced signal X shown in FIG. 10 is input to thereproduced signal processing apparatus 300 of this embodiment, thepattern predictor 303 creates a predicted value P and judges whether thepredicted value P matches the previously set specific pattern or not,and the prediction filter 302 outputs the reproduced signal X as it isas a prediction filter output in a portion where the predicted value Pof the reproduced signal changes to “−25”, “0”, “25”, and the predictionfilter 302 outputs the corresponding predicted value P, instead of thereproduced signal X, as a prediction filter output except in the portionwhere the predicted value P of the reproduced signal changes to “−25”,“0”, “25”, on the basis of the judgement result.

Thus, the prediction filter 302 eliminates non-linear distortion of thewaveform of the input reproduced signal X and can supply a signal havingno non-linear distortion (a prediction filter output) to the adaptiveequalizer 301 in the post stage.

Then, the adaptive equalizer 301 adaptively equalizes the predictionfilter output in which the non-linear distortion has been eliminated,thereby obtaining waveform-equalized output Y.

Then, while in the above description, as the filtering processingperformed by the prediction filter 302, the prediction filter 302outputs the reproduced signal X as it is as a prediction filter outputin a portion where the predicted value P of the reproduced signalchanges to “−25”, “0”, “25”, and outputs the corresponding predictedvalue P, instead of the reproduced signal X, as a prediction filteroutput except in the portion where the predicted value P of thereproduced signal changes to “−25”, “0”, “25”, on the basis of thejudgement result from the pattern predictor 303, the component of thespecific frequency band of the reproduced signal X is cut except in theportion where the predicted value P of the reproduced signal changes to“−25”, “0”, “25”, thereby outputting the resultant signal, as an exampleof another filtering method performed by the prediction filter 302.

Hereinafter, a detailed description will be given using FIGS. 9 and 11.FIG. 11 is a diagram for explaining filtering performed by theprediction filter in the reproduced signal processing apparatusaccording to the modification of this second embodiment.

The reproduced signal processing apparatus 300 according to themodification of the second embodiment comprises a prediction filter 302,an adaptive equalizer 301, and a pattern predictor 303 like theabove-described construction of the second embodiment shown in FIG. 9.The prediction filter 302 according to the modification of the secondembodiment cuts the component of the specific frequency band of theinput reproduced signal X according to the judgement result and outputsthe resultant signal, and the prediction filter 302 is constructed as,for example, a digital filter as shown in FIG. 14. Then, the coefficientW_(n) of the digital filter which is the prediction filter 302 may befixed or adaptively updated as in the first embodiment, and anycoefficient may be used as long as the coefficient has a characteristicfor eliminating the influence of the non-linear distortion of thewaveform of the input reproduced signal X. Further, while in the secondembodiment, the judgement result and the predicted value P are outputfrom the pattern predictor 303 to the prediction filter 302, only thejudgement result may be output in the modification of the secondembodiment. The other construction is similar to that of the reproducedsignal processing apparatus according to the second embodiment describedabove, and a description is omitted here.

Next, an operation of the reproduced signal processing apparatus 300according to the modification of the second embodiment having theabove-described construction will be described using FIG. 11. Initially,when the reproduced signal X as shown in FIG. 11 is input to thereproduced signal processing apparatus 300, the pattern predictor 303predicts the predicted value P of the reproduced signal X and outputsthe judgement result on the basis of the predicted value P. Then, theprediction filter 302 receives only the judgement result from thepattern predictor 303, and performs filtering for the reproduced signalX on the basis of the judgement result. Here, a judgement result signalB shown in FIG. 6 is taken as an example.

The prediction filter 302 outputs the input reproduced signal X as it isas a prediction filter output in a portion where the predicted value Pof the reproduced signal changes to “−25”, “0”, “25”, while theprediction filter 302 cuts the component of the specific frequency bandof the reproduced signal X and outputs the resultant signal as aprediction filter output instead of outputting the reproduced signal Xexcept in the portion where the predicted value P of the reproducedsignal changes to “−25”, “0”, “25”.

Thus, the prediction filter 302 according to the modification of thesecond embodiment performs filtering processing for cutting thecomponent of the specific frequency band of the reproduced signal X in aportion where the predicted value P of the reproduced signal changes to“−25”, “0”, “25”, and even when the component of the same band as thatof the signal whose frequency is to be cut is included in a portionwhere the predicted value P of the reproduced signal changes to “−25”,“0”, “25”, the prediction filter 302 does not cut the component.

Thus, the prediction filter 302 securely eliminates the non-lineardistortion of the waveform of the input reproduced signal X and cansupply waveform having little non-linear distortion to the adaptiveequalizer 301 in the post stage.

Then, the output of the prediction filter in which the non-lineardistortion has been eliminated as described above, is adaptivelyequalized by the adaptive equalizer 301, thereby obtaining awaveform-equalized output Y.

As described above, in the second embodiment, the prediction filter 302subjects the reproduced signal X to filtering, and thereafter theadaptive equalizer 301 adaptively equalizes the reproduced signal whichwas subjected to the filtering. Therefore, even when the reproducedsignal X input to the reproduced signal processing apparatus 300 of thisembodiment has a waveform of non-linear distortion on which a frequencycomponent of the same band as that of the normal waveform issuperimposed as described with reference to FIG. 16, the failure inwaveform equalization due to the non-linear distortion is eliminated,and thereby the influence of waveform distortion on thewaveform-equalized output Y can be suppressed. As a result, in thereproduced signal processing apparatus 300 according to the secondembodiment, a preferable equalization characteristic can be obtained andthe reproduced signal X can be always subjected to optimal adaptiveequalization.

APPLICABILITY IN INDUSTRY

The reproduced signal processing apparatus and reproduced signalprocessing method of the present invention are extremely useful becausethey realize optimal equalization for coping with non-linear distortionwhich is partly caused due to production variances in medium such as anoptical disk and a magnetic disk, or the like.

1. A reproduced signal processing apparatus for equalizing a waveform ofa reproduced signal which is reproduced from a recording medium,comprising: a digital filter for equalizing the reproduced signal; acoefficient updater for adaptively updating coefficients for determiningan equalization characteristic of the digital filter; a patternpredictor for predicting a data sequence of the reproduced signal andoutputting a predicted value of the reproduced signal, and judgingwhether or not the data sequence of the reproduced signal is apreviously set specific pattern, thereby to output the judgement result;and a selection circuit for selecting one of the output of the digitalfilter and the predicted value of the reproduced signal as awaveform-equalized output, and outputting the selected one.
 2. Thereproduced signal processing apparatus as defined in claim 1, whereinthe selection circuit selects the output of the digital filter when thejudgement result indicates that the data sequence of the reproducedsignal is the specific pattern, and selects the predicted value when thejudgement result indicates that the data sequence of the reproducedsignal is not the specific pattern.
 3. The reproduced signal processingapparatus as defined in claim 1, wherein the coefficient updater updatesthe coefficients of the digital filter when the judgement resultindicates that the data sequence of the reproduced signal is thespecific pattern, and does not update the coefficients of the digitalfilter when the judgement result indicates that the data sequence of thereproduced signal is not the specific pattern.
 4. The reproduced signalprocessing apparatus as defined in claim 1, wherein the coefficientupdater adaptively updates the coefficients of the digital filter usingthe predicted value.
 5. The reproduced signal processing apparatus asdefined in claim 1, wherein the digital filter equalizes the reproducedsignal into multiple values and outputs the equalized signal, and thespecific patterns which are previously set in the pattern predictor areportions in which the data sequence of the reproduced signal changesfrom a minimum value up to a maximum value and in which it changes fromthe maximum value up to the minimum value.
 6. The reproduced signalprocessing apparatus as defined in claim 1, wherein the digital filterequalizes the reproduced signal into multiple values and outputs theequalized signal, and the specific pattern which is previously set inthe pattern predictor is a portion in which the data sequence of thereproduced signal is other than the minimum value and the maximum value.7. The reproduced signal processing apparatus as defined in claim 5,wherein the pattern predictor predicts the data sequence of thereproduced signal using partial response equalization, and judgeswhether the predicted data sequence of the reproduced signal matches thespecific pattern or not.
 8. A reproduced signal processing apparatus forequalizing a waveform of a reproduced signal which is reproduced from arecording medium, comprising: a pattern predictor for judging whether ornot the data sequence of the reproduced signal is a previously setspecific pattern, thereby to output the judgement result; a predictionfilter for partially performing filtering on the reproduced signal onthe basis of the judgement result; and an adaptive equalizer foradaptively equalizing the output of the prediction filter.
 9. Thereproduced signal processing apparatus as defined in claim 8, whereinthe pattern predictor outputs a judgement result as to the data sequenceof the reproduced signal and predicts the data sequence of thereproduced signal to output the predicted value of the reproducedsignal; the prediction filter outputs the reproduced signal when thejudgement result indicates that the data sequence of the reproducedsignal is the specific pattern; and outputs the predicted value of thereproduced signal when the judgement result indicates that the datasequence of the reproduced signal is not the specific pattern.
 10. Thereproduced signal processing apparatus as defined in claim 8, whereinthe filtering processing performed by the prediction filter is toeliminate a specific frequency band from the waveform of the reproducedsignal only when the judgement result indicates that the data sequenceof the reproduced signal is not the specific pattern.
 11. The reproducedsignal processing apparatus as defined in claim 8, wherein the specificpatterns which are previously set in the pattern predictor are portionsin which the data sequence of the reproduced signal which is predictedby the pattern predictor changes from a minimum value up to a maximumvalue and in which it changes from the maximum value up to the minimumvalue.
 12. The reproduced signal processing apparatus as defined inclaim 8, wherein the specific pattern which is previously set in thepattern predictor is a portion in which the data sequence of thereproduced signal which is predicted by the pattern predictor is otherthan the minimum value and the maximum value.
 13. A reproduced signalprocessing method for equalizing a waveform of a reproduced signal whichis reproduced from a recording medium, comprising: an adaptiveequalization step of adaptively equalizing the reproduced signal withupdating coefficients for determining an equalization characteristic ofthe waveform, thereby to output the equalized signal; a prediction stepof predicting the data sequence of the reproduced signal and outputtingthe predicted value of the reproduced signal; a judgement step ofjudging whether or not the data sequence of the reproduced signal is apreviously set specific pattern, thereby to output the judgement result;and a selection step of selecting one of the output of the equalizationstep and the output of the prediction step as a waveform-equalizedoutput, and outputting the selected one.
 14. A reproduced signalprocessing method for equalizing a waveform of a reproduced signal whichis reproduced from a recording medium, comprising: a judgement step ofjudging whether or not the data sequence of the reproduced signal is apreviously set specific pattern, thereby to output the judgement result;a filtering step of partially performing filtering on the reproducedsignal on the basis of the judgement result; and an adaptiveequalization step of adaptively equalizing the output of the filteringstep.
 15. The reproduced signal processing apparatus as defined in claim6, wherein the pattern predictor predicts the data sequence of thereproduced signal using partial response equalization, and judgeswhether the predicted data sequence of the reproduced signal matches thespecific pattern or not.